With development of communication technologies, a mobile communication system has developed a System Architecture Evolution (SAE) system.
FIG. 1 is a schematic diagram illustrating a structure of an existing SAE system according to the related art.
Referring to FIG. 1, the system includes an Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) 101 that includes a Core Network (CN) of a Mobile Management Entity (MME) 105 and a Serving GateWay (S-GW) 106. The E-UTRAN 101 is configured to connect a User Equipment (UE) to the core network, and further includes at least one evolved Node B (eNB) 102 and one Home Node B (HeNB) 103, and optionally includes a Home evolved Node B GateWay (HeNB GW) 104. The MME 105 and S-GW 106 may be implemented in one module or be divided for independent implementation. Herein, eNB 102s connect with each other through an X2 interface and connect with MME 105 and S-GW 106 through an S1 interface. The HeNB 103 directly connects with MME 105 and S-GW 106 through the S1 interface. Alternatively, the HeNB 103 connects with the optional HeNB GW 104 through the S1 interface, and then HeNB GW 104 connects with MME 105 and S-GW 106 through the S1 interface.
In an early stage of establishment of a SAE system or in an operation process of the SAE system, configuring the SAE system to optimize parameters consumed significant manpower and material resources, especially the setting for a wireless parameter to ensure a good coverage and capacity, mobility robustness, mobility load balancing, and an access speed for the UEs. In order to save the manpower and material resources configurations cost in the operation of the SAE system, at present, a self-optimization method for SAE system is proposed. During a process of self-optimization, a configuration for an eNB or a HeNB is optimized according to a current state of the SAE system. Hereinafter the eNB and HeNB are referred to as an eNB respectively to describe the self-optimization method for SAE system.
FIG. 2 is a schematic diagram illustrating a basic principle for performing a self-optimization to a SAE system according to the related art.
Referring to FIG. 2, after an eNB is powered on or accesses a SAE, the eNB may perform a self-configuration process. The self-configuration process includes a basic configuration for the eNB and an initial radio parameter configuration. Herein, the basic configuration for the eNB includes configuring an Internet Protocol (IP) address for the eNB and detecting the Operation, maintenance and Management (OA&M), authentication between the eNB and the core network and downloading a parameter of software and operations of the eNB for self-configuration. When the eNB is a HeNB, it is also needed to detect to which HeNB GW the HeNB belongs. The initial radio parameter configuration is implemented in accordance with experiences or simulations and performance of each eNB within the SAE system will be influenced by environment of an area where the eNB is located, thus the eNB needs to initialize the radio parameter configuration according to the environment of the area where the eNB located, and performs an initial configuration for a neighbor list and an initial configuration for load balancing. After the self-configuration process is completed, parameters configured by the eNB are not optimal and, in order to achieve a better performance in the SAE system, it is necessary to optimize or adjust the configuration of the eNB, which is also known as a self-optimization of the mobile communication system. When the configuration of an eNB is optimized or adjusted, it may be performed by the eNB controlled by a back-stage OA&M, which a standardized interface may exist between the OA&M and the eNB. The OA&M sends a parameter to be optimized to the eNB (which may be an eNB or a HeNB) through the interface and the eNB optimizes the parameter. Of course, the parameter optimization may also be performed by the eNB itself, i.e., the eNB detects that the performance is to be optimized and then optimizes or adjusts a corresponding parameter. Optimization or adjusting for the configuration of an eNB may include self-optimization for a neighbor list, self-optimization for coverage and capacity, self-optimization for mobility robustness, self-optimization for load balancing and self-optimization for a parameter of a Random Access CHannel (RACH), etc.
Currently, a basic principle of self-optimization for mobility robustness within version 10 is that, when a UE encounters a RLF or a handover failure, the UE indicates that an RLF report is available when the UE re-enters a connection mode. The network sends a message to the UE to request the RLF report, wherein the RLF report sent by the UE includes an E-UTRAN Cell Global Identifier (ECGI) of a cell last serving the UE, an ECGI of a cell trying to re-establish, an ECGI of a cell last triggering a handover process, the time from the last triggering handover to a connection failure, a reason of the connection failure is a RLF or a handover failure, and a radio measurement. A base station obtaining the RLF report forwards the RLF report to a base station located where the cell last serving the UE. The base station last serving the UE determines whether it is a too early handover, or a too-late handover, or handing over to a wrong cell, or overwriting a vulnerability. If the RLF report indicates a too early handover or handing over to a wrong cell, the base station sends information about the too early handover or a handover to a wrong cell to a base station that triggered the too early handover or handing over to a wrong cell.
However, when an existing mechanism is applied to a RLF detection or a handover failure detection in inter-Radio Access Technologies (inter-RAT), if it is necessary for a UE to report a RLF report to a third Generation mobile communication system (3G) or a second Generation mobile communication system (2G), there are a relatively large impact on a UE of 3G and 2G.
A method for reducing the impact on a terminal of 2G/3G is, when a problem cell is a 3G cell or a 2G cell, and/or a cell trying to re-establish firstly after a failure also is a 3G cell or a 2G cell, a UE does not send a RLF report to a Radio Network Controller (RNC)/Base Station System (BSS). The RNC or BSS detects a reason of the failure itself. However, the method has problems as follows.
Problem 1: For a RLF failure, when a UE reestablishes a Radio Resource Control (RRC) connection to a RNC, a UE identifier sent to the RNC by the UE may not be a UE identifier saved in the RNC, so that the RNC could not find UE context and could not obtain historical information of the UE, thereby a reason for the RLF failure could not be detected.
Problem 2: For a handover between 2G and LTE, such as a procedure in which 2G executes a Cell Change Order (CCO) to a UE to LTE, which does not result from a RLF, a source RNC could not distinguish between the RLF and the CCO.
Problem 3: for a too early handover from 3G/2G to LTE, a RNC needs to detect a reason for a failure itself. In order to support other cases in future, such as a wrong cell handover from 3G/2G to LTE, it is still necessary for a UE to send a RLF report to the LTE. An eNB sends a handover report to the RNC after detecting the reason for the failure; therefore the RNC will count the same failure event repeatedly.
Problem 4: When a RNC for establishing a RRC connection when a UE backs to the 3G/2G is different from a source RNC before a handover, how to detect a reason of a failure.
Problem 5: for a successful handover from 3G/2G to LTE, a RLF occurs in a UE soon, then the UE accesses back to 3G/2G to establish a RRC connection, a problem of whether a RLF report is sent from the UE to a LTE base station is unclear. If the RLF report is not reported, an operation of an existing UE will be influenced. If the RLF report is reported, some information is not obtained. How to report and how an eNB to deal with the RLF report after receiving it are all unclear problems.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.